82. Fossils of a 300-Million-Year-Old Forest Found

“The woods are lovely, dark and deep,” Robert Frost wrote when moved by the sight of a contemporary forest. But a coal mine in Illinois has revealed woods that, if not lovelier, are certainly darker and deeper—and a good bit older.

“You can walk in a single direction for a long distance, through this bizarre Lord of the Rings, cathedral-like thing,” says Scott Elrick, a geologist with the Illinois State Geological Survey, who studied the 300-million-year-old fossilized forest. “As you look up, you see gray flat shale, impressions on that shale, or entire trees, or tree stumps. . . . It’s the worm’s-eye view. You’re looking up at what the forest floor used to look like.”

The fossil ceiling, held up by 6-foot-high, 80-foot-wide pillars of coal, goes on for 4 square miles. No other known preserved forest comes close in size. And thanks to tidal rhythms, the mud deposited on top of this forest is layered, so years can be counted as with the rings of a tree. The 15 feet of sediment that blankets the fossils was laid down in four months—instantaneously in geologic time. The mine runs along a fault line, leading Elrick to surmise that an earthquake dropped one side of the fault and caused flooding. Because the subsequent influx of sediment was “not a catastrophic tsunami thing but more of a slow-motion event, all the small itty-bitty plants are in place.”

The slow pace at which that mud flowed in preserved an incredible diversity of flora. “We had lycopod trees 6 feet wide and 100 feet long, ground cover things, sphagnum moss, delicate little ferns next to these big, huge, honking trees. It’s crazy—we haven’t seen anything like this before,” Elrick says. At the moment, no one else is likely to see it either: The mine, now empty of coal, is closed.